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Cell Wall
The cell wall is a non-living intracellular component of the bacterial cell that resides inside the glycocalyx. It makes up 20 to 40% of the dry weight of an organism. Function The cell wall prevents plasmoptysis, or bursting of the bacterial cell. The bacteria is usually hypertonic to its surroundings, or in a hypotonic environment, and therefore has water flowing into its cell, creating a turgor pressure. Without a cell wall, the turgor pressure would cause the cell membrane to burst. With the cell wall, the bacteria is turgid, like a tire. *If the surroundings were isotonic, less water would flow in, and the cell would become flaccid. *If the surroundings were hypertonic, then water would flow out of the cell, causing plasmolysis. **Cell membrane shrinks, but cell wall does not. The cell wall is responsible for the shape of the bacteria. If the cell wall was removed, all bacteria would be spherical. The cell wall provides an attachment site for flagella, which rotates like a propeller. The cell wall filters bigger molecules out of the bacteria. It is structured and works in a similar fashion to a sieve or screen door. Chemistry The structural component of the cell wall is murein, also known as peptidogylcan. In murein, there are two types of amino sugars: *NAM = N-acetylmuramic acid **Unique to bacteria *NAG = N-acetyalglucosamine **Also found in chitin, which is found in fungi and crustaceans Control Penicillin and Cephalosporin Penicillin targets murein synthesis by inhibiting peptide interbridges between the NAM molecules. It attaches to the transpeptidase, which is the acive site of the NAM molecule that allows it to bond with itself. Penicillin works best when bacteria are growing, but will also work during normal cell maintenance or remodeling. Cephalosporin works in the same way. As a result, the target cell's cell wall weakens and the cell then dies from plasmoptysis. Both are chemotherapuetic agents and magic bullets. 'Lysozyme' Lysozyme is an enzyme found in tears and saliva. Lysozymes work by breaking the bond between a NAM and a NAG. 'Alcohols and Detergents' Alcohols and detergents do not attack the cell wall. Instead, they attack the second membrane of the cell of Gram-negative bacteria. Outer Membrane The outer membrane is a membrane only found in Gram-negative bacteria, which acts as the main barrier while murein is more used for structure. Even though LPS is part of the cell wall, it does NOT stop plasmolysis or give the cell structure. It makes up about 80% of the Gram-negative bacteria's cell wall. The outer membrane is made up of lipopolysaccharides (LPS), while the (inner) cell membrane is made up of phospholipoproteins. Both work in the same way in that they regulate what materials travel through the cell, and LPS is very seletive. The LPS makes Gram-negative bacteria more likely to block some antibiotic such as penicillin. LPS also protects against detergents, bile, meavy metals, and lysozyme. When LPS breaks down, it releases endotoxin, which can cause a fatal shock or a fever, depending on the concentration. Periplasmic Space In Gram-positive bacteria, the pericplasmic space is the space between the cell membrane and the cell wall. In Gram-negative bacteria, it's the space between the cell membrane and the outer membrane, which includes a murein layer. The periplasmic space contains periplasm and all the enzymes made for the remodeling of the cell wall, such as penicillin binding protein.